Rotationally symmetrical hollow compound body

ABSTRACT

A rotationally symmetrical compound body make by centrifugal casting in which the metal to be cast is poured with the aid of a rotating or stationary casting device disposed axially in a rotating drum either radially or tangentially onto the endless fibers, stable fibers or fiber matting abutting at the inner wall of the drum, whereby the outer fiber-reinforced layers of the compound body adjoining the wall of the drum are heated and cool off to room temperature only after the cooling off of the inner metallic layers; the thermal coefficient of expansion of the inner metallic layers is equal to or smaller than that of the outer layers.

United States Patent [191 Zechmeister ROTATIONALLY SYMMETRICAL HOLLOW COMPOUND BODY [75] Inventor: Hartwin Zechmeister, Munich,

Germany [73] Assignee: Maschinenfabrik Augsburg-Nurnberg AG, Munich, Germany [22] Filed: Apr. 19, 1972 [21] Appl. No.: 245,575

[30] Foreign Application Priority Data Apr. 19, 1971 Germany 2118848 [52] U.S. Cl 29/191.2, 29/l91.4, 164/114,

[51] Int. Cl B32b 15/00 [58] Field of Search 29/19l.4, 191.2

[5 6] References Cited UNITED STATES PATENTS 1,280,909 10/1918 Wales et a1. 29/191.4 X

[ Nov. 109, 1974 Primary Examiner-A. B. Curtis Attorney, Agent, or Firm-Craig & Antonelli [5 7] ABSTRACT A rotationally symmetrical compound body make by centrifugal casting in which the metal to be cast is poured with the aid of a rotating or stationary casting device disposed axially in a rotating drum either radially or tangentially onto the endless fibers, stable fibers or fiber matting abutting at the inner wall of the drum, whereby the outer fiber-reinforced layers of the compound body adjoining the wall of the drum are heated and cool off to room temperature only after the cooling off of the inner metallic layers; the thermal coefficient of expansion of the inner metallic layers is equal to or smaller than that of the outer layers.

3 Claims, 1 Drawing Figure The present invention relates to rotationally symmetrical hollow compound bodies made by centrifugal casting.

It is generally known to make pipes, hearings or the like of metallic or plastic materials according to the centrifugal casting process. It is further known in the prior art to manufacture in this manner fiberreinforced plastic cylinders which are utilized predomi nantly as stationary parts, for example, as masts. The prior art centrifugal casting processes, however, are not suited for the manufacture of boilers or of rapidly revolving pipes, drums, or rolls because a compound body manufactured in this manner has an inadequate bonding strength and admits of high radial deformations and distortions. The bond between fiberreinforcement and matrix is insufficient, for example, in the case of a centrifuging drum of a centrifuge rotating or spinning at high circumferential speeds which has as a consequence a separation, ripping or bulging of the components.

Based on this recognition, the present invention seeks to provide a rotationally symmetrical compound body whose metal matrix is reinforced with metallic or non-metallic fibers, which assures a safe bonding between the individual components constituting the compound body also at high circumferential speeds, at high internal pressures and temperatures. Furthermore, the compound body is to possess a low density notwithstanding a high degree of compression. Moreover, the radial deformation or distortion and bulging of the compound body is to be as small as possible in operation in order to permit its use, for example, for such applications as gas centrifuges. It is another paramount consideration for the manufacture of compound bodies that they be free from cavities and impurities or contaminations.

The underlying problems are solved according to the present invention as described hereinabove in that the metal to be cast is poured by means ofa rotating or stationary casting device which is axially arranged in a rotating drum, radially or tangentially onto the endless fibers, staple fibers or fiber matting lying essentially in the circumferential direction against the drum wall, whereby the outer fiber-reinforcing layers of the compound body adjacent the drum wall are heated and cool off to room temperature only after the cooling off of the inner metallic layers, whose thermal coefficient of expansion is equal to or lower than that of the outer layers.

The present invention is suited, on the one hand, if the matrix material of the fibers and the metallic material forming the inner layers are identical (for example, consist ofan aluminum alloy) and therefore possess the same thermal coefficient of expansion.

The same effect is also achieved if the thermal coefficient of expansion of the outer metal matrix (for example, an aluminum alloy) is greater than the thermal coefficient of expansion of the inner plain-metal material, (for example, a nickel alloy).

Further features of the present invention will become apparent from the following description. The advantage of the present invention resides in that a homogeneous, dense compound body free from cavities is produced in which the bonding between individual components is high. The metal sprayed from the nozzles of the casting device is selectively directed whereby a dense ramiform grain structure is achieved in a predominantly tangential direction, which is again improved in that as a result of the proposed cooling conditions, i.e., to cool off the outer fiber-reinforced layer only after the inner plain-metal layer, a residual stress condition is attained at room temperature which is indicative of tangentially directed tensile stresses on the outside and tangentially directed compressive stresses on the inside.

It is also feasible within the scope of the present invention that the outer fiber-reinforced layers (for example, a nickel alloy) have a smaller thermal coefficient of expansion than the inner layers (for example, an aluminum alloy). In that case, the outer layers, for example, carbon fiber-reinforced Ni super alloys upon cooling freeze in the radial direction so that a heating during the rotation would not fulfill the requisite purpose. It is thereby proposed in accordance with the present invention to undertake the rotation for such length of time--without additional heating of the outer zones--until the inner layers (with the higher thermal coefficients of expansion) have solidified and hardened so that at room temperature a residual stress condition in the tangential direction is also produced. A significant characteristic of the present invention resides as to the rest with the use of these materials in that during the cooling off of the compound body, compressive stresses are set up in the axial direction in the outer fiber-reinforced layers and tensile stresses in the inner metallic layers. If the outer layers consist, for example, of a nickel alloy reinforced with carbon fibers and the inner layer of a plain (non-reinforced) aluminum alloy, then--as already mentioned above--the thermal coefficient of expansion is smaller on the outside than at the inside; during cooling the inner layers will tend to c0ntract axially against the essentially frozen outer layers. An axial residual stress condition is built-up thereby which imparts to the compound body particularly fa vorable properties when subjected to alternating bending loads, for example, with the use as centrifuging drum or the like since under bending the outer layers now subjected to tension are prevented from tearing thanks to the compressive preload.

The present invention is further characterized in that the transition of the outer layer to the inner layer is progressive, i.e., produces a drifting transition therebetween, and in that a clinch of both forceand form locking type is produced. A compound body with this residual or inherent stress condition will not readily yield, i.e., will permit only small radial deformations under rotation or with the application of an internal pressure. Therebeyond, a compound body is produced by the present invention which is suited for high temperature used and in which the fibers are incorporated very firmly in the matrix. Of course, proper consideration must be given thereby that the requirement for fiber stability in high temperature applications limits the choice among suitable material systems to those that have phase diagrams which preclude or minimize compounding, diffusive reaction with the matrix and internal oxidation. Considering these factors, for example, the following systems are suited for the process of manufacture of the rotationally symmetrical body in accordance withthe present invention: carbon fibers or tungsten fibers in Ni -super alloys, or beryllium fibers in aluminum alloys. Furthermore, the possibility exists to optimize the bond and compression of the components to the different intended applications by a corresponding adjustment of the rotational speeds of the drum and of the casting device. Another advantage afforded by this invention resides in that the possibility exists to admix in the course of the casting process different matrix materials so that a compound body consisting of different layers can be produced, for example, of different layers the specific modulus E of which may vary in magnitude from one layer to the next. Thus, for the use of the compound body as centrifuging drum, it will be desirable to cause the specific modulus E, i.e., the ratio of modulus E to density, to increase from the inside toward the outside of the body. The bonding properties of such a compound body are considerably superior to those of a wound body. Compound bodies in accordance with the present invention are suited, for example, for applications as revolving drums in centrifuges, as containers, as bearings and rolls or as combustion chambers or thrust nozzles in rockets. In the manufacture of rocket nozzles, it may be advisable to admix condensation coolants such as graphite.

The apparatus utilized in to the present invention essentially consists in that a rotating or stationary casting device extends into a drum whose bottom carries, for example, a drive pin or trunion, whereby radial or tangential nozzles are provided in the longitudinal direction of the casting device.

These and further objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein:

The single FIGURE is a schematic cross-sectional view of an apparatus in accordance with the formation of the rotationally symmetric body of the present invention, by means of which the process for producing the present invention can be realized.

The present invention will be explained, for example, by reference to the schematic drawing while the manufacturing process will be described in detail by reference to one embodiment of the apparatus.

Referring now to the single FlGURE of the drawing, reference numeral 2 designates a cylindrical drum totating about a vertical axis and closed off by means of a bottom 1. A casting device 3 extends axially into the cylindrical drum 2. The casting device 3 consists of a cylindrical barrel on which are provided diammetrically oppositely disposed nozzles 4 extending in the longitudinal direction. A tubular member 5 terminates from above in the barrel; a mixing chamber 6 is arranged ahead of the tubular member 5, into which are fed the desired metals or alloy constituents (arrows A and B) for the corresponding alloy formation. A heating device in the form of a heating coil 7 may be arranged extending along the center line of the casting device 3. The nozzles 4 or slots may conveniently be arranged either radially or tangentially in the barrel shroud. Arranged centrally on the bottom 1 of the drum 2 is an axially extending pin or trunion 8 which serves for the drive and support of the drum 2. The schematically indicated bearing is designated by reference numeral 9. A heating device 10 is inserted into the wall ofthe drum 2. The drum 2 is enclosed by a ring 11. The entire apparatus is surrounded by a shroud or jacket 12 (shown in dash lines) so that the casting operation can take place optionally in an evacuated or inert gas environment.

The process for the present invention can be explained readily after the description of the apparatus. The fibers 13, for example, beryllium fibers in the form of staple fibers are inserted essentially circumferentially in several rows into a skeleton frame of matrix material hugging the wall of the drum. For example, fiber matting may be optionally inserted in a like manner. The matrix material 14, for example, an aluminum alloy, is fed into the mixing chamber 6 in liquid state, is homogenized therein, possibly mixed with a wetting agent so that an alloy enters the rotating casting device at a constant temperature and free from inclusions. Once in the casting device, the matrix material is centrifuged through the nozzles against the rotating inner drum wall where it immediately envelopes the fibers and forms a dense compound body as a result of the high centrifugal forces which occur at that time. The heating device arranged in the wall of the drum keeps the compound body at an elevated temperature. In the course of the rotary casting operation, after a dense layer has been deposited by centrifuging on the fibers, another metal 15, for example, with a slightly higher specific modulus E but of approximately equal coefficients of expansions such as an aluminum titanium alloy, which compounds with the previously deposited metal matrix under proper conditions, may then be poured. These conditions have to be adjusted depending on the desired application of the compound body. For example, with the application of the body as flywheel, the outer layer should have a specific gravity higher than that of the inner layer. After termination of the casting operation of the metal through the nozzles, the rotation of the drum is maintained for such length of time until the inner layers are cooled off approximately to room temperature. A solidification of the inner layers may occur as a result of continued rotation under proper conditions. It is only thereafter that according to the present invention the outer layers which are essentially still plastic, are slowly cooled off to room temperature.

This produces a shrink-fit which additionally makes for an intimate meshing and interlocking of the inner and outer layers. The stress conditions which result thereby can be influenced or optimized without difficulty, for example, by changing the drum wall temperature. The melting and centrifugal casting in an evacuated or inert gas environment entails the known advantages; it then becomes practicable to produce in this manner materials having maximum purity together with specific chemical and physical properties without having to fear cavities, oxidation and similar imperfections in the compound material.

Typical examples for the casting alloy materials which can be used with the method according to the present invention are those described in the German standards DIN-NORM 1725, sheet 2, for example, for the Al-alloys material Nos. 3.2151 and 3.2l53, which are alloys of the type G-AlSi Cu containing in percent by weight 5.0 to 7.5 of Si, 3.0 to 5.0 of Cu, 0.3 to 0.6 of Mn, 01 to 0.3 of Mg and the rest essentially Al (except for the indicated permissive quantities of admixtures see in particular material No. 32153.01)

and of the type G-AlSi Cu containing in percent by weight 6.0 to 8.5 of Si, 2.0 to 3.5 of Cu, 0.2 to 0.6 of

Mn, 0.1 to 0.3 of Mg and the rest essentially Al. These German standards are edited by the Deutscher Normenausschuss, Koln, Kamekestrasse, West Germany, and/or West Berlin, Burggrabenstrasse, and are printed by Beuth-Vertrieb, Koln, Kamekestrasse, West Germany, through whom these standards are available. (The standards referred to herein were in effect as of April 19, 1971.) The present invention is also applicable in particular to pressure casting or die casting alloys, for example, the Al-alloy materials Nos. 3.2582 and 3.3292 described in the aforementioned German standards, which are alloys of the type GD-AlSi containing in percent by weight 11.0 to 13.5 of Si, to 0.4 of Mn and the rest essentially Al (except for indicated permissive admixtures--see in particular material No. 3.258205) and of the type GD-AlMg containing in percent by weight 7.0 to 10.0 of Mg, 0 to 2.5 of Si, 0.2 to 0.5 of Mn and the rest essentially Al (except for indicated permissive admixtures-see in particular material No. 3.329205). Typical examples of titanium containing Al-alloys are those casting alloys described in the same German standards, for example, material Nos. 3.1841 and 3.1371 which are alloys of the type G AlCu Ti, containing in percent by weight 4.5 to 5.2 of Cu, 0.15 to 0.30 of Ti and the rest essentially Al (except indicated permissive admixtures--see in particular material No. 31841.63) and of the type G-AlCuJiMg, containing in percent by weight 4.2 to 4.9 of Cu, 0.15 to 0.30 of Mg, 0.15 to 0.30 of Ti and the rest essentially Al (except for indicated permissive admixtures--see in particular material No. 3.l37l.6l

A typical example of the apparatus according to this invention and of the method of operating the same are as follows:

The cylindrical drum consists of a high heat-resistant steel, for example, of material No. 1.4922 (X20CrMoVl2-l) or of material No. 1.4981 (X8CrNiMoNb 16--16) as described in the aforementioned German standards, has a diameter of 1 in. max. and is rotated with a circumferential velocity of about v 50-200 mlsec. The casting temperature of the Alalloys is about 650 C 700 C. The duration of rotation 1,, is dependent on the desired degree of compression of the compound body and on the cooling-off time of the compound body with an unheated and with a heated drum. However, on the average I is about l-30 min.

The foregoing are merely representative values and materials to which this invention is applicable. However, it is understood that the present invention is applicable also to numerous other materials as known to those skilled in the art and as used heretofore in connection with analogous prior art methods. For example, conventional nickel alloys or conventional Nisuperalloys may also be used, for example, as the outer or inner plain metal material.

Thus, while I have shown and described only one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art. For example, it is quite apparent that various modifications are possible as regards material selection and construction without departing from the spirit of the present invention. For example, it may be of advantage for the manufacture of compound bodies of large bearings to arrange the casting device in the drum to be axially displaceable so that the casting device moves from one end of the drum to the other during the casting operation. Any suitable means of known construction may be used to obtain the suitably controlled displacement of the casting device. A compound body can be made by a corresponding selection of the casting material and matching of the feed of the casting device and rotational speed of the drum as well as the cooling conditions, which exhibit the optimum properties desired for the particular application. Obviously, the use of a further bearing of the drum is necessary with the use of a longer drum for the manufacture of longer compound bodies. Thus, it is quite apparent that the present invention is not limited to the details shown and described herein, and I therefore do not wish to be limited to the details shown and described but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

1 claim:

1. Rotationally symmetrical hollow compound body consisting of two layers, arranged one within the other, each part merging into the other without gaps, and characterized by the combination of the following features:

a. the inner layer essentially consists of metal selected from the group consisting of alloys on a nickel, titanium, cobalt or aluminum basis;

b. the outer layer essentially consists of a fibrous material selected from the group essentially consisting of tungsten, beryllium, steel, boron, carbon or silicon carbide fiber, which are: arranged as coiled endless fiber, staple fiber or fiber matting, whereby the spaces between the individual fibers are cast with one of the metals mentioned under (a), thereby providing a low density structure;

c. said materials of the outer and inner layers being selected such that the heat expansion coefficient of the metal inner layer is equal to or larger than that of the outer layer, and said material of said outer layer exhibits a specific modulus less than the specific modulus of said material of the inner layer; and

d. when the compound body is at rest the outer layer shows evidence mainly of tensile stress, the inner layer mainly of pressure stress so that the compound body exhibits small radial deformations under rotation or with the application of an internal pressure.

2. A compound body according; to claim 1, wherein said outer layer is fibrous material of beryllium being cast with an aluminum alloy, and said inner layer is an aluminum-titanium alloy providing an approximately equal heat expansion coefficient to said outer layer.

3. A compound body according; to claim 11, wherein said outer layer is a fibrous material of carbon being cast with a nickel alloy, and said inner layer is an aluminum alloy providing a larger heat expansion coefficient than said outer layer. 

1. ROTATIONALLY SYMMETRICAL HOLLOW COMPOUND BODY CONSISTING OF TWO LAYERS, ARRANGED ONE WITHIN THE OTHER, EACH PART MERGING INTO THE OTHER WITHOUT GAPS, AND CHARACTERIZED BY THE COMBINATION OF THE FOLLOWING FEATURES: A. THE INNER LAYER ESSENTIALLY CONSISTS OF METAL SELECTED FROM THE GROUP CONSISTING OF ALLOYS ON A NICKEL, TITANIUM, COBALT OR ALUMINUM BASIS; B. THE OUTER LAYER ESSENTIALLY CONSISTS OF A FIBROUS MATERIAL SELECTED FROM THE GROUP ESSENTIALLY CONSISTING OF TUNGSTEN, BERYLLIUM, STEEL, BORON, CARBON OR SILICON CARBIDE FIBER, WHICH ARE ARRANGED AS COILED ENDLESS FIBER, STAPE FIBER OR FIBER MATTING, WHEREBY THE SPACES BETWEEN THE INDIVIDUAL FIBERS ARE CAST WITH ONE OF THE METALS MENTIONED UNDER (A), THEREBY PROVIDING A LOW DENSITY STRUCTURE; C. SAID MATERIALS OF THE OUTER AND INNER LAYERS BEING SELECTED SUCH THAT THE HEAT EXPANSION COEFFICIENT OF THE METAL INNER LAYER IS EQUAL TO OR LARGER THAN THAT OF THE OUTER LAYER, AND SAID MATERIAL OF SAID OUTER LAYER EXHIBITS A SPECIFIC MODULUS LESS THAN THE SPECIFIC MODULUS OF SAID MATERIAL OF THE INNER LAYER; AND D. WHEN THE COMPOUND BODY IS AT REST THE OUTER LAYER SHOWS EVIDIENCE MAINLY OF TENSILE STRESS, THE INNER LAYER MAINLY OF PRESSURE STRESS SO THAT THE COMPOUND BODY EXHIBITS SMALL RADIAL DEFORMATION UNDER ROTATION OR WITH APPLICATION OF AN INTERNAL PRESSURE.
 2. A compound body according to claim 1, wherein said outer layer is fibrous material of beryllium being cast with an aluminum alloy, and said inner layer is an aluminum-titanium alloy providing an approximately equal heat expansion coefficient to said outer layer.
 3. A compound body according to claim 1, wherein said outer layer is a fibrous material of carbon being cast with a nickel alloy, and said inner layer is an aluminum alloy providing a larger heat expansion coefficient than said outer layer. 